Plasma CVD apparatus and dry cleaning method of the same

ABSTRACT

In a parallel flat plate type plasma CVD apparatus, plasma damage of constituent parts in a reaction chamber due to irregularity of dry cleaning in the reaction chamber is reduced and the cost is lowered. In the parallel flat plate type plasma CVD apparatus in which high frequency voltages of pulse waves having mutually inverted waveforms are applied to an upper electrode and a lower electrode, and the inversion interval of the pulse wave can be arbitrarily changed, the interior of the reaction chamber is dry cleaned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 10/752.520, filed on Jan. 8, 2004, now U.S. Pat. No. 7,223,446,which is a divisional application of U.S. application Ser. No.09/818,188, filed on Mar. 26, 2001, now U.S. Pat. No. 6,675,816, whichclaims the benefit of a foreign priority application filed Japan, onMar. 27, 2000, as Ser. No. JP 2000-087474.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a parallel flat plate type plasma CVDapparatus, and particularly to a parallel flat plate type plasma CVDapparatus having a structure suitable for dry cleaning in a reactionchamber and a dry cleaning method thereof.

2. Description of the Related Art

In fabrication of various semiconductor devices or the like, as methodsof forming thin films, there are a sputtering method using a sputteringphenomenon under reduced pressure, a vacuum evaporation method using anevaporation phenomenon, a plasma CVD (Chemical Vapor Deposition) methodusing low temperature gas decomposition by plasma, a thermal CVD methodusing heat decomposition of a gas, a photo-CVD method for decomposing agas by energy of short wavelength light or ultraviolet rays, and thelike. Among these, in the plasma CVD method, a gas easy to decompose andcontaining an element of a thin film to be formed is supplied into areaction chamber under reduced pressure, high frequency electric poweris supplied between electrodes to generate plasma, and the supplied gasis activated by the plasma, so that an objective thin film can be formedat a low temperature. This method is used for thin film formation of anamorphous silicon film, a silicon oxide film, a silicon nitride film orthe like.

However, an objective thin film is adhered to not only a surface of anobject to be treated, but also a wall surface of the reaction chamber, asurface of the electrode, a shielding member, and the like. As anaccumulated film thickness increases, the adhered film peels off fromthe wall surface of the reaction chamber, the surface of the electrode,the shielding member, and the like, so that particles are produced inthe reaction chamber. Thus, there occurs a problem that the producedparticles adhere to the surface of the object to be treated so that thesurface is polluted and the yield is lowered. Accordingly, it isnecessary to remove the adhered film when the thickness of the filmadhered to the wall surface of the reaction chamber, the surface of theelectrode, the shielding member, and the like reaches a predeterminedaccumulated film thickness, or when an operating time reaches apredetermined time. As one of methods of this removing, for example,there is dry cleaning in which an etching gas is introduced into thereaction chamber and is activated by plasma similarly to the thin filmformation, and the adhered film is removed by plasma etching.

An example of the dry cleaning using the plasma etching will beexplained using a parallel flat plate type plasma CVD apparatusschematically shown in FIG. 1A.

A first electrode 102 as a high frequency voltage application electrodeand a second electrode 103 as a ground electrode are provided in areaction chamber 101. The reaction chamber is kept under reducedpressure by a vacuum exhaust system 110 including a turbo molecular pump108, a dry pump 109, and the like. Heaters (not shown) are attached tothe first electrode and the second electrode, and a temperaturecondition suitable for the dry cleaning is kept. An etching gas used forthe dry cleaning is controlled by a mass flow controller 107 to have agas flow suitable for the dry cleaning, and is supplied into thereaction chamber through a valve 106 (hereinafter, they are collectivelyreferred to as an etching gas supply line). Then, a high frequencyvoltage is supplied from a high frequency power supply 104 through amatching circuit 105 to the first electrode 102 to generate plasma, andthe dry cleaning by etching is carried out. Here, since the highfrequency power supply is connected to the first electrode, and thesecond electrode is grounded, the applying voltage waveform of the highfrequency voltage becomes as schematically shown in FIG. 2A. Note, timefor one period is determined as t second.

In the plasma CVD apparatus as shown in FIG. 1A, at the time of thinfilm formation, in order to make temperature in the reaction chamber anexcellent thin film formation condition, there is a case where heatertemperatures of the first electrode and the second electrode are set todifferent values. Besides, since the high frequency voltage is suppliedto the first electrode and the second electrode is grounded, thedeposition mechanisms of films adhered to the wall surface of thereaction chamber, the surface of the electrode, and the like becomedifferent from one another, so that the film qualities and accumulatedfilm thicknesses are also different. Further, also in the case where thedry cleaning by the plasma etching is carried out, by the same factor,the etching mechanisms become different among the wall surface of thereaction chamber, the surface of the electrode, and the like, so thatetching speeds are also different, and removal of the adhered films isirregular.

For example, in the plasma CVD apparatus as shown in FIG. 1A, theadhered films are etched and removed in the order of FIGS. 3A, 3B and3C. That is, the films are removed in the order of the second electrode,the wall surface of the reaction chamber from the vicinity of the secondelectrode to the vicinity of the first electrode, and the firstelectrode, that is, with directionality from the second electrode to thefirst electrode. It appears that this is caused since in the case of thefirst electrode, although a chemical etching progresses by a chemicalreaction of an active radical and the adhered film, in the case of thesecond electrode, a small number of ions exist together with the activeradical, and in addition to a chemical etching by those ions, a physicaletching by a sputtering effect is also added. Since the adhered films onthe second electrode, in the vicinity of the second electrode, and thelike are removed in this way earlier than the first electrode, they areforced to receive plasma irradiation in the state where the surfaces areexposed, so that the damage by plasma has been serious.

Besides, since the removal of the adhered films is irregular, a timerequired to completely remove the adhered films becomes long, andsuperfluous gas, electric power and the like are consumed by that.

SUMMARY OF THE INVENTION

The constitution of the present invention is a parallel flat plate typeplasma CVD apparatus and a dry cleaning method thereof, which ischaracterized by including a matching circuit, a first change-overswitch, and a pulse amplitude modulation circuit between a highfrequency power supply and a first electrode and between the highfrequency power supply a second electrode, and an inverter circuit, asecond change-over switch, and a wiring line for ground between thefirst change-over switch and the second electrode.

The dry cleaning method of the parallel flat plate type plasma CVDapparatus is such that after an etching gas is supplied into a reactionchamber, pulse amplitude modulated high frequency voltages are appliedthrough the pulse amplitude modulation circuit to the first electrodeand the second electrode. At this time, the phase of the pulse amplitudemodulated high frequency voltage applied to the second electrode isshifted by 180° with respect to the first electrode through the invertercircuit.

Besides, in accordance with irregularity in the adhesion of adheredfilms in the reaction chamber, that is, in accordance with irregularityin the film quality and accumulated film thickness of the adhered filmsin the reaction chamber, and in accordance with irregularity in plasmaetching, a pulse interval of a signal wave for pulse amplitudemodulation is arbitrarily selected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views respectively showing a structure ofa conventional parallel flat plate type plasma CVD apparatus and aparallel flat plate type plasma CVD apparatus of the present invention.

FIGS. 2A and 2B are views respectively showing a waveform of a voltageapplied to an electrode from a high frequency power supply in theconventional parallel flat plate type plasma CVD apparatus and in theparallel flat plate type plasma CVD apparatus of the present invention.

FIGS. 3A to 3C are views showing a removal process of adhered films byplasma etching in the conventional parallel flat plate type plasma CVDapparatus.

DETAILED DESCRIPTION OF THE INVENTION

A mode for carrying out the present invention will be described withreference to FIGS. 1B and 2B.

FIG. 1B schematically shows a plasma CVD apparatus of the presentinvention. Its constitution, such as a structure in a reaction chamber,an etching gas supply line, and a vacuum exhaust system, is the same asthe conventional plasma CVD apparatus of FIG. 1A, and this plasma CVDapparatus is also the same as the conventional plasma CVD apparatus inthat an etching gas is supplied from the etching gas supply line intothe reaction chamber to generate plasma and dry cleaning is carried outby plasma etching. The different point from the conventional plasma CVDapparatus of FIG. 1A is an application method of a high frequencyvoltage at the time of dry cleaning, that is, a generating method ofplasma.

Specifically, although pulse amplitude modulated high frequency voltagesare applied to the first electrode 102 and the second electrode 103, thehigh frequency voltage whose phase is shifted by 180° with respect tothe first electrode 102 is applied to the second electrode 103. By this,the relation of a high frequency voltage application electrode and aground electrode between the first electrode 102 and the secondelectrode 103 is alternately inverted. For that purpose, as shown inFIG. 1B, a pulse amplitude modulation circuit 114 and an invertercircuit 111 are provided in a line for applying the high frequencyvoltage from a high frequency power supply 104. Besides, in general, atthe time of thin film formation, since the first electrode 102 is madethe high frequency voltage application electrode, and the secondelectrode 103 is made the ground electrode, there are providedchange-over switches 112 and 113 for changing over the relation of thehigh frequency voltage application electrode and the ground electrodebetween the time of thin film formation and the time of dry cleaning.For example, when switches 201-204 are respectively switched OFF, ON,ON, and OFF, it becomes possible to alternately invert the relation ofthe high frequency voltage application electrode and the groundelectrode between the first electrode 102 and the second electrode 103,so that the dry cleaning can be carried out. When the switches 201-204are respectively switched ON, OFF, OFF, and ON, the first electrode 102can be made the high frequency voltage application electrode, and thesecond electrode 103 can be made the ground electrode, so that the thinfilm formation can be carried out.

The dry cleaning is carried out in such a manner that after the etchinggas is supplied into the reaction chamber from the etching gas supplyline under reduced pressure, the pulse amplitude modulated highfrequency voltages are applied to the first electrode and the secondelectrode from the high frequency power supply to perform plasmaetching. The high frequency voltages applied to the first electrode andthe second electrode have phases shifted by 180° from each other by theinverter provided between the high frequency power supply and the secondelectrode. Here, a time in which a voltage (ON voltage) is applied tothe first electrode to make it the high frequency voltage applicationelectrode and a voltage (OFF voltage) is applied to the second electrodeto make it the ground electrode is made “a”, a time in which the voltage(ON voltage) is applied to the second electrode to make it the highfrequency voltage application electrode and the voltage (OFF voltage) isapplied to the first electrode to make it the ground electrode is made“b”, and a/(a+b) is made a duty ratio of a pulse wave. This duty ratiois arbitrarily selected in accordance with irregularity in the adhesionof the adhered films in the reaction chamber, that is, in accordancewith irregularity in the film quality and accumulated film thickness ofthe adhered films in the reaction chamber, and in accordance withirregularity in plasma etching, so that the adhered films can beuniformly removed. Specifically, it is sufficient if a pulse width of asignal wave for pulse amplitude modulating a high frequency voltage isarbitrarily selected. Incidentally, it is not always necessary that theOFF voltage is set to 0 V, but a slight voltage may be applied. Matchingof a traveling wave and a reflected wave of plasma is performed by amatching circuit 105 at each place in FIG. 2B where a pulse wave rises,and this matching becomes easy by applying the slight voltage.

In the manner described above, plasma damage of the wall surface and theelectrode in the reaction chamber caused by the irregularity in the filmquality and accumulated film thickness of the adhered films in thereaction chamber and the irregularity in the plasma etching isprevented. Besides, hitherto, a treatment time is superfluously longsince there is a portion where the removing process is slow. However,since the adhered films can be uniformly removed, a treatment time canbe shortened and the consumption of gas, electric power and the like isreduced.

Embodiment

An embodiment of the present invention will be described with referenceto FIG. 1B. Here, it is assumed that films adhered to the wall surface,the electrodes and the like in the reaction chamber are silicon oxidefilms, and a dry cleaning method at the time when a presumed accumulatedfilm thickness of this adhered silicon oxide film reaches apredetermined film thickness at which dry cleaning is required, will bedescribed.

The temperature in the reaction chamber, that is, the set temperature ofheaters (first heater and second heater) attached to the first electrodeand the second electrode is made the same condition as the time when thesilicon oxide film as an object to be removed is formed. By this, itbecomes unnecessary to take a time for adjusting the temperature in thereaction chamber to perform the dry cleaning. Here, the first heater andthe second heater were respectively made 300° C. Of course, since theset temperatures of the adhered films at the time of film formation arerespectively different, and there is also a case where the temperaturesare set to different values between the first heater and the secondheater, the temperature in the reaction chamber at the time of the drycleaning is not limited to this. Besides, according to the film qualityof the adhered film, temperature adjustment may be performed to set thetemperature to a value suitable for the dry cleaning.

First, in order to avoid danger by a chemical reaction in exhaustpiping, the exhaust piping is changed over from piping dedicated for athin film forming gas to piping dedicated for an etching gas by a valve(not shown) . Thereafter, the vacuum exhaust system 110 is used toevacuate the reaction chamber to a predetermined pressure. During this,an interval between the first electrode 102 and the second electrode 103is set to a condition suitable for plasma generation. Here, it was made25 mm. When the pressure is reduced to the predetermined pressure, next,a N₂ purge is carried out under a pressure of 1.07 ×10 ² Pa and a flowof 200 SCCM. Then, evacuating is again performed to reduce the pressureto a predetermined value.

In the manner described above, an unreacted gas and the like remainingin the piping system in the CVD apparatus is removed to performcleaning. After cleaning of the piping system is performed, NF₃ as theetching gas for the dry cleaning is supplied into the reaction chamberthrough the control valve 106 after the flow is controlled by the massflow controller 107 to 100 SCCM, and the pressure is adjusted to a valuesuitable for the dry cleaning. Here, the pressure was made 1.33 ×10¹ Pa.

Next, pulse amplitude modulated high frequency voltages are applied tothe first electrode 102 and the second electrode 103 from the highfrequency power supply 104 to generate plasma so that the dry cleaningis performed by plasma etching. Before the high frequency voltages areapplied, the change-over switches 112 and 113 for changing over avoltage application method to the electrodes are previously changed overfrom one for thin film formation to one for dry cleaning. Besides, inaccordance with irregularity in the adhesion of the adhered films in thereaction chamber, that is, in accordance with irregularity in the filmquality and accumulated film thickness of the adhered films in thereaction chamber, and in accordance with irregularity in the plasmaetching, the pulse interval (duty ratio) of a signal wave is arbitrarilyset in the pulse amplitude modulation circuit. The operation of changingover the voltage application method and the setting of the duty ratiomay be carried out at any time before the voltage is applied. Here, thevoltage application method for the thin film formation is a method inwhich the first electrode 102 is made the high frequency voltageapplication electrode and the second electrode 103 is made the groundelectrode. The voltage application method for the dry cleaning is amethod in which pulse amplitude modulated high frequency voltages areapplied to the first electrode 102 and the second electrode 103, thewaveform of the high frequency voltage applied to the second electrode103 becomes a waveform whose phase is shifted by 180° with respect tothe first electrode 102, and the relation of the high frequency voltageapplication electrode and the ground electrode is inverted with apredetermined period between the first electrode 102 and the secondelectrode 103.

After the dry cleaning by the plasma etching is ended, the reactionchamber is evacuated to a predetermined pressure by using the vacuumexhaust system 110. Next, a N₂ purge is carried out under a pressure of1.07 ×10² Pa and a flow of 200 SCCM. Then, evacuating is again carriedout to reduce the pressure to a predetermined value. By this, anunreacted gas and the like remaining in the piping system in the CVDapparatus is removed to carry out cleaning. During this, the intervalbetween the first electrode 102 and the second electrode 103 is made toreturn to the initial value.

In the manner described above, the films adhered to the wall surface ofthe reaction chamber, the electrodes, and the like of the plasma CVDapparatus are uniformly removed to prevent plasma damage of the wallsurface of the reaction chamber, the electrodes, and the like, and atreatment time is shortened. Incidentally, in this embodiment, themethod of dry cleaning for removing the silicon oxide film has beendescribed, the present invention can also be applied to a thin film suchas an amorphous silicon film or a silicon nitride film formed by usingthe parallel flat plate type plasma CVD apparatus by arbitrarilyselecting conditions. Besides, the conditions such as pressure andtemperature at the time of the dry cleaning are not limited to thosedisclosed in this embodiment, but may be arbitrarily selected.

According to the present invention, since films adhered to the wallsurface of the reaction chamber, electrodes and the like as constituentparts in the reaction chamber can be uniformly removed, plasma damage ofthe constituent parts in the reaction chamber due to irregular plasmaetching can be suppressed, and the consumption of gas and electric powercan be suppressed by shortening of the treatment time, so that the costof the dry cleaning to remove the films adhered to the constituent partsin the reaction chamber can be reduced.

1. A method comprising: introducing an etching gas into a plasma CVDreaction chamber including a first electrode and a second electrode;generating a plasma of the etching gas by a high frequency power supply;and cleaning an inside of the plasma CVD reaction chamber by a plasmaetching, wherein a first pulse amplitude modulated high frequencyvoltage is applied to the first electrode by the high frequency powersupply and a second pulse amplitude modulated high frequency voltage isapplied to the second electrode by the high frequency power supply, andwherein the second pulse amplitude modulated high frequency voltage hasan opposite phase to the first pulse amplitude modulated high frequencyvoltage.
 2. The method according to claim 1, wherein the second pulseamplitude modulated high frequency voltage is phase shifted from thefirst pulse amplitude modulated high frequency voltage by an invertercircuit.
 3. A method comprising: forming a film by a plasma CVD in aplasma CVD reaction chamber including a first electrode and a secondelectrode; introducing an etching gas into the plasma CVD reactionchamber; generating a plasma of the etching gas by a high frequencypower supply; and cleaning an inside of the plasma CVD reaction chamberby a plasma etching, wherein a first pulse amplitude modulated highfrequency voltage is applied to the first electrode by the highfrequency power supply and a second pulse amplitude modulated highfrequency voltage is applied to the second electrode by the highfrequency power supply, and wherein the second pulse amplitude modulatedhigh frequency voltage has an opposite phase to the first pulseamplitude modulated high frequency voltage.
 4. The method according toclaim 3, wherein the second pulse amplitude modulated high frequencyvoltage is phase shifted from the first pulse amplitude modulated highfrequency voltage by an inverter circuit.
 5. A method comprising:introducing an etching gas into a plasma CVD reaction chamber includinga first electrode and a second electrode; generating a plasma of theetching gas by a high frequency power supply; and cleaning an inside ofthe plasma CVD reaction chamber by a plasma etching, wherein a firstpulse amplitude modulated high frequency voltage is applied to the firstelectrode by the high frequency power supply and a second pulseamplitude modulated high frequency voltage is applied to the secondelectrode by the high frequency power supply, and wherein the secondpulse amplitude modulated high frequency voltage is phase shifted fromthe first pulse amplitude modulated high frequency voltage at 180°. 6.The method according to claim 5, wherein the second pulse amplitudemodulated high frequency voltage is phase shifted from the first pulseamplitude modulated high frequency voltage by an inverter circuit.
 7. Amethod comprising: forming a film by a plasma CVD in a plasma CVDreaction chamber including a first electrode and a second electrode;introducing an etching gas into the plasma CVD reaction chamber;generating a plasma of the etching gas by a high frequency powersupplly;and cleaning an inside of the plasma CVD reaction chamber by aplasma etching, wherein a first pulse amplitude modulated high frequencyvoltage is applied to the first electrode by the high frequency powersupply and a second pulse amlitude modulated high frequency voltage isapplied to the second eletrode by the high frequency power supply, andwherein the second pulse amplitude modulated high frequency voltage at180°.
 8. The method according to claim 7, wherein the second pulseamplitude modulated high frequency voltage is phase shifted from thefirst pulse amplitude modulated high frequency voltage by an invertercircuit.